JPH02217615A - Magnetic bearing controller - Google Patents

Abstract

PURPOSE:To stably hold a floating object in a floating state by adding a first signal to a second signal, and feeding back the signals to an electromagnet via a position feedback gain and controller for a magnetic bearing. CONSTITUTION:Signals from a position sensor 1L constituting a magnetic bearing 6L are divided into two and separated, and one is fed as a first signal 1L to the input terminal (+) of an addition circuit 9L. Characteristic frequency components which may cause instability are extracted from the other signal by a band-pass filter 7L, and then the signal is amplified by a proportional circuit 8L having alpha-times gains, and thereafter it is inputted as a second signal bL for a magnetic bearing 6R to the input terminal (+) of an addition circuit 9R. Signals from a position sensor 1R constituting a bearing 6R are also divided into two and separated in the same way, and one is fed to an addition circuit 9 and the other is fed to the addition circuit 9L of the other bearing 6L via a band-pass filter 7R and a proportional circuit 8R. The signal cL after addition is inputted to a control circuit 3L via a position feedback gain 2L.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic bearing for high-speed rotating bodies such as molecular pumps, compressors, turbines, and spindles for machine tools.

[Conventional technology]

There are magnetic bearings that use electromagnets as a means of keeping rotating bodies and moving objects floating. This magnetic bearing has less loss than conventional fluid-lubricated bearings, allows for a dry bearing and a cleaner atmosphere, and is particularly useful in vacuum conditions.

In this magnetic bearing, as a means of setting the floating position of a rotating body or a running object, the floating position of the floating object is measured, and based on the measurement signal, the current value to be passed through the electromagnet is determined, and the magnitude of the magnetic force generated from the electromagnet is determined. There is a means to determine.

FIG. 8 is a block diagram showing the configuration of the control system of the means. In FIG. 8, the position sensor 1 detects the position of the floating object f(
An example of such a sensor is an eddy current displacement meter. The position feed pack gain 2 is a rounding value that proportionally multiplies the magnitude of the signal obtained by the positional sensor 1 to the required magnitude. The control circuit 3 consists of a rounded signal processing circuit that inputs a signal obtained with a position feedback gain of 2 to the electromagnet 4 in an appropriate form. Examples of this signal processing circuit include a PID (proportional-integral-differential) circuit, a phase compensation circuit, and a combination circuit thereof. The electromagnet 4 is a coil wound around an iron core.
The magnetic force for levitation is generated in accordance with the current supplied from the control circuit 3.

Considering the simplest position feedback system in which the control circuit 3 is composed of only proportional elements (P and X), the transfer function between the electromagnet 40 input I and the output magnetic force F is determined by the resistance and inductance of the coil, iron core, etc. It becomes a first-order lag system with less than Yoshishi.

F/I − to /(1+Tw −8)
...(1) Here, KM is 'electromagnet 4
, TM is the time constant of the electromagnet 4, and S is the Lagras operator. Therefore, the transfer function from the measured displacement of the position feedback system to the force F to the floating object is as follows.

F/D-1 et al. K, -KM/(1+TM-8)
(2) Here, K represents the proportional gain of the position feedback gain 2, and K represents the proportional gain of the control circuit 3. Position feed force (force F)/
In order to see the frequency characteristics of (displacement D), the Lagras operator S
-12 is set as f and substituted into equation (2). Here, f is the frequency (Hz) and is j-fl-. Let (force F)/(displacement D) be a complex number as follows.

F/D”Km(f)+j −Kt(f) ・
...(3) In equation (3), the real part of (force F)/(displacement D) means the stiffness that depends on the frequency f, and the imaginary part is the frequency f
means attenuation dependent on . The imaginary part of the first-order lag as shown in equation (2) is always negative, which causes a destabilizing force on the floating object that is opposite to damping.

Figure I@9 is a diagram showing the relationship between (force F)/(displacement D), that is, the value of the imaginary part of equation (3), and frequency f.

The dotted line person shown in FIG. 9 corresponds to equation (2),
The above state is shown. If the value of the frequency f-fe shown in Figure 9 is larger than the damping of the natural frequency fc of the floating object and the position feedback system, especially the damping of the floating object, the natural frequency will be photographed in a divergent manner. and become unable to drive.

Therefore, the position feed system (force F)/(displacement D)
In order to provide a damping effect to the control circuit 3, a proportional element (P
A differential element (D element) or a phase compensation element is provided in parallel with the D element. Here, a differential element (D element) will be taken as a representative example. When the differential element (D element) is implemented as a circuit in the control circuit 3, the following first-order lag system is added, resulting in a round shape.

(Differential element) ””Ko-8/(1+TD-8)
...(4) Here, K is the gain of the differential element,
TD is a time constant. The (force F)/(displacement D) of the differential element [74-Dopak system] is expressed as follows.

F/D-K, ・KD-KM-8/((1+TD-8)
(1+TM-3) )...(5) Since the numerator of equation (5) is the first order of S and the denominator is the second order of S, the imaginary part of equation (5) is the dashed line B shown in Figure 9. It's like K. In other words, in order to maintain the position of a floating object, which has a damping effect on the floating object in a low frequency region and a destabilizing effect in a high frequency region, the control circuit 3 requires the coexistence of a proportional element and a differential element. Is required. The (force F)/(displacement D) of the position feed system of the control circuit 3 is as follows: (KP+KD-V(1+TD-8))・K
, /(1+TM-8) (6), and has almost the same characteristics as the solid line C shown in FIG. 9 and the dashed-dotted line B described above. If the natural frequency fc consisting of the floating object and the position feeder system is placed in a low frequency range that has a damping effect, stability can be ensured and operation can be performed without generating vibrations.

When a magnetic bearing having such characteristics is used as the bearing 6 of the rotating body 5 shown in FIG. 10(a) and the rotating body 5 is levitated, the following phenomenon occurs. The rotating body 5 is shown in FIG. 10 (b) (C) (d) (・) (f) ~
It has a natural frequency on the infinite side as shown in . The damping caused by the material of the rotating body s itself acts as a destabilizing effect for the natural vibration frequency below the rotation speed, and acts as a damping effect for the natural vibration frequency above the rotation speed.

Therefore, it is necessary to bring the natural frequency of the magnetic bearing 6's position feedback system below the rotational speed to a frequency range that has a damping effect of (force F)/(displacement D). However, the natural frequency of the rotating body 5 is as shown in Fig. 10 (bJ (e) (
d) (・) (f) Since there are infinite numbers as shown in ~, there is always a natural frequency in the frequency range that has the destabilizing effect of (force F)/(displacement D). Therefore, even with the damping of the natural frequency of the rotating body 5 itself, if the destabilizing effect of the position feedback system of the magnetic bearing 6 increases, it becomes unstable, and the vibration increases divergently, making it difficult to rotate. become unable.

[Problem to be solved by the invention]

As mentioned above, in the conventional system, in order to maintain the position of the floating object, the position of the floating object is measured by the position sensor J, the signal is fed back, and force is generated from the electromagnet 4. This force becomes a destabilizing force that causes the floating object to vibrate. Even if processing such as PrD and phase compensation is performed in the control circuit 3, it becomes a stabilizing (damping) force in the low frequency band, but it still has a large destabilizing force in the middle and high frequency bands. However, in a floating object such as a rotating body that has a natural frequency on the infinite side, the natural frequency always exists in the frequency a band that causes a destabilizing force, so the magnetic bearing 6 generates divergent vibrations. This is K.

In particular, the third-order natural frequency, which is usually higher than the maximum rotational speed of the rotating body 5, has a small damping ability and is easily vibrated in a destructive manner due to the destabilizing effect of the position feedback system of the magnetic bearing.

As a countermeasure, even if the damping area is extended to the 3rd natural frequency using a magnetic bearing, it will cause a greater destabilizing effect in the higher frequency range, and the 4th natural frequency will diverge. This will cause vibrations.

Therefore, the present invention provides a magnetic bearing that can change the destabilizing force generated by the magnetic bearing into a stabilizing force in a specified frequency band, prevent the generation of divergent vibrations, and stably hold a floating object. The purpose is to provide a control device.

[Means to solve the problem]

A magnetic bearing control device according to the present invention feeds back a signal from a position sensor for a floating object to a magnetic bearing, and actively uses a magnetic bearing. It is equipped with two sets of magnetic bearings each consisting of an electromagnet, a bandpass filter, a proportional circuit, and an adder, and the signal from the position sensor constituting one of the magnetic bearings is used as the first signal, and the signal is set at the magnetic bearing position. On the other hand, the signal from the position sensor of the other magnetic bearing sandwiching an odd number of node points of the vibration mode of the natural frequency is passed in series through a bandpass filter and a proportional circuit having a center frequency near the natural frequency. 2 signals, and a signal obtained by adding the first signal and the second signal is fed back to the electromagnet via the feedback gain of the magnetic bearing and the control circuit.

[Effect]

By taking the above-mentioned measures, the following effects are achieved. In other words, with respect to the destabilizing force in the high frequency band that the position feedback system of the magnetic bearing has, only the natural frequency component that becomes the destabilizing force is extracted by a band-pass filter with its phase inverted, and this is extracted by the proportional circuit. After being amplified by
0° difference). As a result, all forces generated by the magnetic bearing are converted into stabilizing forces.

Note that Table 1 shows a comparison with the prior art.

(Part 1) (Part 3) table (Part 2) 〔Example〕 Examples of the present invention are shown in FIGS. 1 to 7.

FIG. 1 is a block diagram showing a first embodiment of the present invention, that is, the configuration of a control system related to stabilization of the destabilizing force by the secondary natural frequency of bending.

In FIG. 1, 7 is a band-pass filter that passes the natural frequency component that becomes a destabilizing force, 8 is a proportional circuit that amplifies the signal, and 9 is an adder circuit. 6L and 6R indicate two sets of magnetic bearings (first and second magnetic bearings).

The signal from the position sensor 7L that constitutes the magnetic bearing 6L is 2.
and one of the signals remains as the first signal a.
The other signal is supplied to the (+) input terminal of the adder circuit 9L as L, and the other signal is passed through a bandpass filter 7L to extract the natural frequency component that serves as a cine stabilizing force, and then to a proportional circuit 8L having a gain multiplied by α. After being amplified, the second signal bL is sent to the other magnetic bearing 6R. ] is supplied to the (+] input terminal of the arithmetic circuit 9R. The signal from the position sensor JR that constitutes the magnetic bearing 6R is similarly separated into two, one being sent to the adding circuit 9R and the other being sent to the band pass filter 7R. The signal C is supplied to the addition circuit 9L of the other magnetic bearing via the proportional circuit 8R.The signal C after the addition is input to the control circuit 3 via the position feedback gain 2.

The operation will be explained below in a simple case where the transfer functions of two magnetic bearings are the same.

FIG. 2 is a diagram showing typical gain characteristics of the bandpass filter 7 of the first embodiment. As shown in FIG. 2, the bandpass filter 7 has a center frequency f near the natural frequency to be stabilized. It has a pass characteristic (gain J) when the frequency f is fo.

FIG. 3 shows the relationship between the rotating body, bearing arrangement, and vibration mode. FIG. 3(a) shows the arrangement relationship between the rotating body 5 and the bearings (6L and 6R), and FIG. 3(b) shows the bending secondary vibration mode of the rotating body 5. Position sensors IL and J
R has an odd number of node points between its sensors (in the example shown, Q
(L, QM, and Q8), the signals from these position sensors have phases inverted from each other.

M4 diagram (a) (b) (eJ is a diagram showing the relationship between (force F)/(displacement D) in each No. 45 path, that is, the value of the imaginary part of equation (3) and frequency f.

FIG. 4(a) is a diagram showing the relationship between (force F)/(displacement D) and frequency f in the path of No. 45 aL of one magnetic bearing 6L, and the low frequency region as shown by the solid line C in FIG. It is assumed that a device capable of providing phase compensation such as exhibiting attenuation is used. Thus, the first, second, and third natural frequencies of the rotating body 5 are located in a frequency range that can provide damping, and the fourth natural frequency is located in a frequency range that provides a destabilizing force.

Assuming that (force F)/(f position) of magnetic bearing θL is expressed by equation (3), in the path of signal aL of WJl, F/D-KR(f) + j・Kx(f)
...(7).

FIG. 4(b) i-t is a diagram showing the relationship between (force F)/(displacement D) and frequency f on the magnetic bearing 6L in the path of signal bR.

The second signal bRf′i The signal of the natural displacement component element 4, which acts as a destabilizing force on the magnetic bearing 6L, has a phase inversion.
=-α・KR(f) jα・K,(f)・
...(8-1)9, and in other frequency bands, F/D -0...(8-2).

Thus, in the path of the second signal bR, the fourth
It provides damping for the next natural frequency, and neither damping nor destabilizing force occurs for the other frequencies in the a-band.

FIG. 4(C) is a diagram showing the relationship between (force F)/(displacement D) and frequency af in the path of the signal eL, which is the sum of the first signal aL and the second signal bR.

Finally, the second signal bR is added to the first signal IL, so in the path of the signal eL, only the F/D in the vicinity of f-f4
-(1-α)・Kl(f+j(1-α)・Kx(0・
...(9-1) In other frequency bands, F/D-KB
(f) + j- to 1(f) ... (9-
2). The polarity of the sign of the value of the above equation (9-1) is reversed if the gain α of the proportional circuit 8R is "1" or more.

In this example, the two position sensors are installed at positions where the loss amplitude values of the vibration modes of the secondary natural frequency of bending are the same. The polarity can be reversed.

Thus, the damping characteristic of the magnetic bearing 6L is as shown by the solid line in FIG. 4(C), and the second-order bending natural frequency f4 is also placed in the region where it has a ripple effect.

Similarly, the other magnetic bearing 6R is placed in a region where the bending secondary natural frequency f4 provides damping.

Therefore, the destabilizing force due to the secondary bending natural frequency is changed to a stabilizing force.

According to this embodiment, first and second.

Although a control circuit that applies damping only to the third natural frequency is used, the destabilizing force at the fourth natural frequency can be changed to a damping force (stabilizing force). Therefore, the medium and high frequency hunting problem of the rotating body 5 is reduced, and the bending 2
It is possible to operate up to the next critical speed (corresponding to the 4th natural frequency).For the 5th and higher natural frequencies, there is almost no problem as the destabilizing force is in the frequency range where it is small. .

FIG. 5 is a block diagram showing a second embodiment of the present invention, that is, the configuration of a control system related to stabilization of the destabilizing force due to the first bending natural frequency.

In FIG. 5, the position sensor IM is provided independently from the two sets of magnetic bearing position sensors 7LIJR, and the band-pass filter 7M extracts the signal of only the frequency component that becomes a destabilizing force. The signals are then amplified by proportional circuits 8L and 8R and supplied as signals bL and bR to the (+) input terminals of adder circuits 9L and 9R of the two sets of magnetic bearings 6L and 6R. The gain characteristics of the bandpass filter 7M are shown in FIG. 2, and the center frequency f0 in this embodiment is set near the first bending natural frequency f3.

Thus, the signal from the position sensor 7L forming the magnetic bearing 6L is supplied as the first signal hL to the (+) input terminal of the adding circuit 9L, and the second signal bL and the first signal aL are added. The signal aL after the addition is input to the control circuit 3L via the position feedback gain 2L.

A similar effect is performed on the magnetic bearing 6R.

For the sake of simplicity, the operation will be described below in the case where the two magnetic bearings have the same transfer function.

FIG. 6 is a diagram showing the relationship between a rotating body, a bearing, and a vibration mode. Figure 6(a) shows the rotating body 5 and bearings 6L and 6R.
FIG. 6(b) is a diagram showing the bending primary vibration mode of the rotating body 5. FIG. Position sensors IL and I
Since M is arranged such that an odd number (in the illustrated example, PLllll) of node points are arranged between its sensors, the signals from these position sensors are inverted in phase with each other.

The transfer function of (force F)/(displacement D) of the magnetic bearing 6L is expressed by equation (9-1) near the bending primary surface frequency f5 and equation (9-2) in other bands.

As for the value of equation (9-1), if the gain α of the proportional circuit 80 is “1” or more, the polarity of the sign is reversed.

By appropriately adjusting r in α, the damping characteristics of the magnetic bearing 6L are set in a region where the bending primary surface frequency f3 provides damping, as shown by the solid line in FIG.

Similarly, for the magnetic bearing 6R, the bending primary surface frequency f3
is placed in the region that provides damping. Therefore, the destabilizing force due to the first-order bending specific silk frequency in the above frequency band is changed to a stabilizing force.

It is assumed that both control circuits sL and sR are capable of providing phase compensation so as to exhibit attenuation in the low frequency region, as shown in Figure 9 @C. Further, it is assumed that the internal damping of the rotating body 5 is strengthened so that the secondary bending natural frequency is stable. Thus, the first and second natural frequencies of the rotating body 6 are placed in a frequency range that provides damping, and the third natural frequency also has damping due to the above-mentioned effect.

Thus, although this embodiment uses a control circuit that damps only the first and second-order natural frequencies, the damping force is applied to the region that acts as a destabilizing force at the third-order natural frequency. (Stabilizing power). Therefore, the rotating body 5
The medium and high frequency hunting problem is reduced, and it is possible to operate up to the first critical bending speed (corresponding to the third natural frequency). Note that for natural frequencies of the fourth order or higher, there is almost no problem if the destabilizing force is stabilized by internal damping of the rotating body 6.

Note that the present invention is not limited to the above embodiments.
For example, in the embodiment described above, the bandpass filter 7, the proportional circuit 8. Although the case where the circuit consisting of the subtracter 9 is provided between the position sensor J, the position feeder, and the feeder 2 is illustrated,
It may also be provided in other parts of the magnetic bearing control system. Furthermore, in order to reduce the destabilizing force, a notch filter whose center frequency is near the frequency of the destabilizing force is generally added in the middle of the conventional path shown in Fig. 8. A combination of the conventional method and the present invention may be used. In that case, the embodiment of the present invention adds a notch filter whose center frequency is near the natural frequency of the destabilizing force in the middle of the path of the signal a in FIG. 1 or 5.

Further, the destabilizing force of two natural frequencies may be stabilized by combining the first embodiment and the second embodiment.

Furthermore, it is obvious that the first embodiment can stabilize the destabilizing force of not only the second-order bending, but also the even-order natural frequencies of the fourth, sixth, etc. bending, so the band-pass filter By selecting multiple center frequencies, all of them can be stabilized.

Similarly, the second embodiment can also stabilize the destabilizing force of not only the first-order bending, but also the odd-numbered natural frequencies of the third, fifth, and so on bending. If a plurality of these band-pass filters are employed, the internal waveform of the rotating body 5 is small for natural frequencies of bending third order or higher, and it is effective when destabilizing force becomes a problem.

Further, the shape of the rotating body 5 is not limited to that shown in FIGS. 3 and 10. In addition, various modifications may be made without departing from the gist of the present invention.

Table 1 shows a comparison with examples of prior art.

〔Effect of the invention〕

Since the present invention is configured as described above, according to the present invention, the signal from the position sensor constituting the magnetic bearing is
The signal from another magnetic bearing position sensor or a newly installed position sensor that has an odd number of node points in the vibration mode of the natural frequency with respect to the magnetic bearing position is centered around its natural frequency. A bandpass filter with a frequency and a proportional circuit are passed in series to obtain a second signal, and the signal obtained by adding the first signal and the second signal is fed to the magnetic bearing, so that the specified It is possible to provide a magnetic bearing control device that can change the destabilizing force into a stabilizing force (damping force) for the frequency components that occur, can prevent the occurrence of divergent vibrations, and can stably hold a floating object floating.

Table 1 shows a comparison with the effects of the prior art.

[Brief explanation of the drawing]

1 to 4 are diagrams showing a first embodiment of the present invention.
The figure is a block diagram showing the configuration of the control system, Figure 2 is a diagram showing the gain-frequency characteristics of the bandpass filter, and Figure 3 is a schematic explanation showing the relationship between the rotating body, magnetic bearing arrangement, and secondary bending vibration mode. 4 are diagrams showing attenuation characteristics in each signal path. 5 to 7 are diagrams showing a second embodiment of the present invention, FIG. 5 is a block diagram showing the configuration of the control system, and FIG. 6 is a rotating body, magnetic bearing arrangement, and bending primary vibration. FIG. 7 is a schematic diagram showing the relationship between modes, and FIG. 7 is a diagram showing the damping characteristics of the magnetic bearing. Figures 8 to 10 are diagrams showing conventional examples. Figure 8 is a block diagram showing the configuration of the control system, Figure 9 is a diagram showing the damping characteristics of the magnetic bearing, and Figure 10 is the rotating body and its It is a figure showing a natural frequency. l...Position sensor, 2...Position feedback gain, 3...Control circuit, 4...Ta stone, 5...Rotating body, 6...Magnetic bearing, 7...Band pass filter , 8
... Proportional circuit, 9... Addition circuit, P, Q... Node point of photographing mode. Applicant ftflf 1 person Patent attorney Suzue Takehiko 1st
Figure (b)] 11 lower] ■ [1st natural frequency]

Claims (1)

[Claims] A magnetic bearing control device that actively uses the magnetic bearing by feeding back a signal from a position sensor for a floating object to the magnetic bearing, comprising: a position sensor, a position feedback gain, a control circuit, an electromagnet, and a band. It is equipped with two sets of magnetic bearings consisting of a pass filter, a proportional circuit, and an adder, and uses the signal from the position sensor that constitutes one of the magnetic bearings as the first signal, and generates a vibration mode of a natural frequency with respect to the position of the magnetic bearing. The signal from the position sensor of the other magnetic bearing sandwiching an odd number of node points is passed in series through a bandpass filter and a proportional circuit having a center frequency near its natural frequency to obtain a second signal. A magnetic bearing control device characterized in that a signal obtained by adding the signal and the second signal is fed back to the electromagnet via a position feedback gain and control circuit of the magnetic bearing.